Telescope Row
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Telescope Row clear sky chart from 2005-11-06 to 2024-01-11.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.
Observation TypeMinimum conditions for hour to be usableOut of hours
Clear of CloudsTransparencySeeingSky Brightness
Planetary:50%(no limit)Average(no limit)Nighttime Hours
Deep Sky:70%Average(no limit)5.9Nighttime Hours
CCD Imaging:70%Below AveragePoor(no limit)Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

PlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
Night
64%
23722
29%
74751
26%
23673
69%
23673
38%
40798

By Month

MonthDays of MonthPlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
January1st to 10thNight
51%
756
19%
2561
19%
756
55%
756
23%
1622
January11th to 20thNight
54%
724
23%
2351
20%
724
60%
724
29%
1411
January21st to endNight
53%
792
26%
2574
24%
792
59%
792
26%
1578
February1st to 10thNight
53%
720
27%
2340
24%
720
61%
720
29%
1374
February11th to 20thNight
50%
700
27%
2161
23%
700
58%
700
28%
1306
February21st to endNight
48%
592
26%
1776
21%
592
56%
592
30%
1094
March1st to 10thNight
44%
720
17%
2044
14%
720
49%
720
22%
1422
March11th to 20thNight
47%
720
24%
1980
20%
720
52%
720
28%
1300
March21st to endNight
47%
792
20%
2127
12%
792
53%
792
29%
1373
April1st to 10thNight
47%
720
22%
1800
11%
720
53%
720
31%
1181
April11th to 20thNight
49%
711
29%
1779
14%
711
55%
711
37%
1099
April21st to endNight
54%
720
29%
1800
12%
720
59%
720
44%
1041
May1st to 10thNight
58%
698
28%
1778
15%
698
62%
698
47%
1001
May11th to 20thNight
68%
457
31%
1519
26%
457
72%
457
44%
716
May21st to endNight
68%
388
28%
1552
26%
388
76%
388
39%
695
June1st to 10thNight
67%
360
30%
1440
29%
360
76%
360
43%
610
June11th to 20thNight
75%
360
36%
1440
40%
360
82%
360
55%
530
June21st to endNight
85%
360
38%
1440
47%
360
90%
360
65%
485
July1st to 10thNight
89%
350
38%
1400
47%
350
92%
350
72%
446
July11th to 20thNight
93%
481
37%
1525
37%
481
93%
481
75%
578
July21st to endNight
91%
591
40%
1674
35%
558
92%
558
69%
696
August1st to 10thNight
83%
537
37%
1602
31%
534
85%
534
59%
715
August11th to 20thNight
90%
680
41%
1748
26%
680
91%
680
75%
791
August21st to endNight
90%
792
43%
1980
28%
792
90%
792
77%
915
September1st to 10thNight
87%
720
45%
1800
32%
720
88%
720
77%
830
September11th to 20thNight
81%
720
44%
1800
34%
720
84%
720
64%
913
September21st to endNight
80%
720
43%
2029
39%
720
85%
720
67%
903
October1st to 10thNight
75%
720
33%
2160
32%
720
82%
720
55%
1006
October11th to 20thNight
72%
720
38%
2160
40%
720
77%
720
49%
1068
October21st to endNight
72%
792
39%
2376
39%
792
78%
792
50%
1165
November1st to 10thNight
66%
740
31%
2277
30%
740
71%
740
40%
1228
November11th to 20thNight
62%
760
30%
2470
27%
760
70%
760
37%
1333
November21st to endNight
61%
760
30%
2569
29%
760
67%
760
35%
1366
December1st to 10thNight
53%
760
24%
2660
21%
760
61%
760
27%
1549
December11th to 20thNight
47%
760
18%
3241
20%
759
53%
759
16%
2258
December21st to endNight
42%
829
14%
4818
17%
817
51%
817
11%
3200

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

Occurrence of each ForecastData
Points
Cloud CoverDay
8%423323346%62%
74679
Night
10%5%24424446%56%
75027
TransparencyDay
26%36%19%26%21%
74397
Night
29%36%17%23%21%
74830
SeeingDay
11%10%23%31%19%6%
14257
Night
12%5%13%32%30%9%
23738

By Month

Percentage Cloud Cover SW (2006-)
Color Meanings:
Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 10thDay
21%7%26%5%34447%38%
1600
11th to 20thDay
13%5%25%5%34436%51%
1621
21st to endDay
16%7%35%43445%7%42%
1782
February1st to 10thDay
18%7%23423446%45%
1620
11th to 20thDay
15%5%245%3446%6%45%
1688
21st to endDay
17%8%25%433445%46%
1480
March1st to 10thDay
17%10%37%5%35%5%5%8%33%
1914
11th to 20thDay
19%8%35%5%45%5%5%8%34%
1980
21st to endDay
15%6%35%5%35%446%43%
2227
April1st to 10thDay
16%6%35%5%34447%43%
2160
11th to 20thDay
13%5%2432345%5%55%
2129
21st to endDay
7%423333348%59%
2160
May1st to 10thDay
6%5%23324447%61%
2178
11th to 20thDay
6%422313436%66%
2371
21st to endDay
6%423324447%61%
2723
June1st to 10thDay
5%423223337%65%
2520
11th to 20thDay
2111212235%80%
2520
21st to endDay
221111223383%
2520
July1st to 10thDay
11111222485%
2520
11th to 20thDay
111121223383%
2378
21st to endDay
1111233484%
2546
August1st to 10thDay
11322223479%
2328
11th to 20thDay
111122486%
2152
21st to endDay
1121212486%
2376
September1st to 10thDay
111111212386%
2160
11th to 20thDay
1112323446%74%
2160
21st to endDay
311122223478%
1926
October1st to 10thDay
4313313336%70%
1800
11th to 20thDay
5%312313347%68%
1800
21st to endDay
6%423323345%64%
1980
November1st to 10thDay
9%5%34435%45%7%53%
1802
11th to 20thDay
9%5%245%35%35%6%54%
1710
21st to endDay
13%5%2332335%7%54%
1606
December1st to 10thDay
12%7%45%5%3445%6%47%
1520
11th to 20thDay
29%9%36%423445%31%
1928
21st to endDay
15%12%47%5%245%5%7%34%
2794
January1st to 10thNight
17%8%35%425%5%6%6%39%
2561
11th to 20thNight
13%7%245%25%5%5%6%45%
2351
21st to endNight
16%6%35%3345%5%6%44%
2574
February1st to 10thNight
17%6%33323346%49%
2340
11th to 20thNight
13%7%344345%5%8%44%
2159
21st to endNight
15%8%25%423446%47%
1776
March1st to 10thNight
19%10%45%425%446%38%
2044
11th to 20thNight
17%8%35%43325%8%40%
1980
21st to endNight
14%7%345%3445%6%45%
2127
April1st to 10thNight
13%8%245%35%5%5%7%43%
1800
11th to 20thNight
10%6%245%23346%53%
1779
21st to endNight
6%5%3332445%9%56%
1800
May1st to 10thNight
45%35%32435%8%58%
1778
11th to 20thNight
5%5%23334449%58%
1519
21st to endNight
4314435%46%9%57%
1552
June1st to 10thNight
4423323348%65%
1440
11th to 20thNight
1122313436%74%
1440
21st to endNight
211221322481%
1440
July1st to 10thNight
11121332482%
1440
11th to 20thNight
1111111235%82%
1576
21st to endNight
11132335%6%75%
1773
August1st to 10thNight
1212424335%72%
1611
11th to 20thNight
111113446%78%
1748
21st to endNight
111213345%79%
1980
September1st to 10thNight
122212225%82%
1800
11th to 20thNight
4313214345%72%
1800
21st to endNight
2312212235%77%
2029
October1st to 10thNight
4313213336%70%
2160
11th to 20thNight
5%423323346%66%
2160
21st to endNight
6%313323345%67%
2376
November1st to 10thNight
10%5%24313347%57%
2277
11th to 20thNight
8%6%244245%6%8%52%
2470
21st to endNight
10%5%14424446%56%
2569
December1st to 10thNight
14%7%245%24346%48%
2660
11th to 20thNight
26%10%345%24447%31%
3276
21st to endNight
17%10%38%6%45%5%46%32%
4862

Transparency (when cloud cover <= 30%)
Color Meanings:
Too cloudy to forecast Poor Below Average Average Above average Transparent
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 10thDay
47%49%22%13%5%
1600
11th to 20thDay
36%39%20%18%14%
1621
21st to endDay
42%48%14%22%10%
1782
February1st to 10thDay
40%35%20%21%11%
1620
11th to 20thDay
39%47%18%24%9%
1697
21st to endDay
42%36%21%20%7%
1480
March1st to 10thDay
49%5%7%18%17%5%
1914
11th to 20thDay
47%5%6%19%17%5%
1980
21st to endDay
42%5%11%20%18%5%
2227
April1st to 10thDay
41%411%19%20%6%
2160
11th to 20thDay
31%5%12%23%23%7%
2132
21st to endDay
25%310%30%25%6%
2160
May1st to 10thDay
22%48%26%32%7%
2178
11th to 20thDay
21%26%30%32%10%
2374
21st to endDay
24%210%31%26%6%
2724
June1st to 10thDay
21%38%26%29%12%
2520
11th to 20thDay
10%27%22%36%24%
2520
21st to endDay
9%2213%32%42%
2520
July1st to 10thDay
6%118%27%56%
2451
11th to 20thDay
8%2310%25%51%
2306
21st to endDay
6%118%31%52%
2405
August1st to 10thDay
12%1211%29%46%
2312
11th to 20thDay
5%1111%34%46%
2152
21st to endDay
6%1112%36%45%
2376
September1st to 10thDay
8%119%31%51%
2160
11th to 20thDay
14%2322%36%23%
2160
21st to endDay
12%2222%38%24%
1926
October1st to 10thDay
17%26%17%30%27%
1800
11th to 20thDay
18%37%20%24%28%
1800
21st to endDay
23%36%18%26%24%
1980
November1st to 10thDay
31%45%21%24%15%
1802
11th to 20thDay
31%49%20%24%12%
1710
21st to endDay
31%28%17%30%12%
1606
December1st to 10thDay
39%48%19%18%13%
1520
11th to 20thDay
56%36%14%15%6%
1928
21st to endDay
50%39%21%13%4
2794
January1st to 10thNight
43%49%21%16%6%
2561
11th to 20thNight
38%49%17%17%15%
2351
21st to endNight
40%5%10%12%18%15%
2574
February1st to 10thNight
38%35%19%21%15%
2340
11th to 20thNight
38%47%17%23%12%
2161
21st to endNight
37%5%7%25%18%8%
1776
March1st to 10thNight
48%48%18%14%7%
2044
11th to 20thNight
43%36%19%20%9%
1980
21st to endNight
39%411%19%19%8%
2127
April1st to 10thNight
38%5%12%18%21%7%
1800
11th to 20thNight
33%38%25%21%10%
1779
21st to endNight
25%5%8%29%26%8%
1800
May1st to 10thNight
24%47%23%29%14%
1778
11th to 20thNight
24%17%23%34%10%
1519
21st to endNight
24%210%27%29%8%
1552
June1st to 10thNight
20%39%24%28%16%
1440
11th to 20thNight
12%36%14%31%34%
1440
21st to endNight
11%1214%30%43%
1440
July1st to 10thNight
7%215%29%56%
1400
11th to 20thNight
7%236%29%52%
1525
21st to endNight
11%218%29%49%
1674
August1st to 10thNight
16%2112%26%44%
1602
11th to 20thNight
9%219%32%47%
1748
21st to endNight
9%118%37%42%
1980
September1st to 10thNight
9%217%24%58%
1800
11th to 20thNight
16%2219%34%28%
1800
21st to endNight
12%2220%33%31%
2029
October1st to 10thNight
17%35%18%24%33%
2160
11th to 20thNight
21%3418%25%29%
2160
21st to endNight
21%2418%29%27%
2376
November1st to 10thNight
28%47%19%22%20%
2277
11th to 20thNight
29%47%21%27%12%
2470
21st to endNight
30%37%18%23%18%
2569
December1st to 10thNight
38%36%17%20%15%
2660
11th to 20thNight
54%38%13%17%6%
3276
21st to endNight
53%410%15%13%5%
4862

Seeing (when cloud cover <= 80%)
Color Meanings:
Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 10thDay
34%11%24%20%10%1
261
11th to 20thDay
21%13%21%27%14%3
341
21st to endDay
19%9%25%26%17%3
374
February1st to 10thDay
22%16%22%21%15%5%
340
11th to 20thDay
22%16%25%26%10%1
387
21st to endDay
23%16%25%26%9%1
346
March1st to 10thDay
26%15%28%23%7%2
420
11th to 20thDay
26%18%19%22%13%3
420
21st to endDay
21%17%32%21%10%
462
April1st to 10thDay
20%16%29%22%13%
420
11th to 20thDay
19%17%30%20%12%1
412
21st to endDay
8%19%28%27%12%6%
420
May1st to 10thDay
13%14%30%29%10%3
423
11th to 20thDay
10%15%32%25%14%5%
448
21st to endDay
10%12%25%30%19%5%
485
June1st to 10thDay
9%10%27%27%18%9%
450
11th to 20thDay
412%28%36%15%5%
450
21st to endDay
25%24%38%22%9%
450
July1st to 10thDay
1318%41%30%7%
446
11th to 20thDay
1113%42%34%10%
444
21st to endDay
113%43%29%15%
487
August1st to 10thDay
2320%38%28%9%
447
11th to 20thDay
1119%40%27%13%
437
21st to endDay
1215%40%32%11%
495
September1st to 10thDay
3316%42%29%7%
450
11th to 20thDay
37%23%40%22%6%
450
21st to endDay
5%7%18%41%25%4
450
October1st to 10thDay
5%11%23%35%20%5%
450
11th to 20thDay
8%8%21%32%24%7%
450
21st to endDay
10%5%26%34%20%5%
495
November1st to 10thDay
11%10%20%28%25%6%
398
11th to 20thDay
9%8%21%30%23%10%
270
21st to endDay
13%9%23%34%17%5%
221
December1st to 10thDay
17%14%16%28%17%7%
180
11th to 20thDay
21%16%16%27%14%7%
180
21st to endDay
25%14%20%22%13%6%
198
January1st to 10thNight
21%7%14%30%20%8%
760
11th to 20thNight
16%6%14%33%22%9%
724
21st to endNight
21%5%12%33%22%7%
792
February1st to 10thNight
20%8%12%32%22%6%
720
11th to 20thNight
19%9%15%31%20%7%
704
21st to endNight
21%7%18%33%18%4
592
March1st to 10thNight
22%9%14%30%20%5%
720
11th to 20thNight
21%7%14%27%24%6%
720
21st to endNight
17%9%19%30%21%3
792
April1st to 10thNight
17%8%18%33%21%4
720
11th to 20thNight
14%10%19%32%20%6%
711
21st to endNight
8%10%23%28%22%9%
720
May1st to 10thNight
7%6%22%32%25%7%
698
11th to 20thNight
9%312%32%36%7%
457
21st to endNight
5%6%14%35%33%7%
389
June1st to 10thNight
5%5%15%34%34%7%
360
11th to 20thNight
15%13%38%37%5%
360
21st to endNight
37%38%45%8%
360
July1st to 10thNight
17%34%49%9%
350
11th to 20thNight
11126%54%16%
481
21st to endNight
11223%55%18%
591
August1st to 10thNight
216%29%50%13%
537
11th to 20thNight
15%35%45%13%
680
21st to endNight
1428%54%13%
792
September1st to 10thNight
227%33%44%13%
720
11th to 20thNight
419%34%40%11%
720
21st to endNight
4310%32%38%14%
720
October1st to 10thNight
6%311%35%34%12%
720
11th to 20thNight
8%49%33%35%11%
720
21st to endNight
7%411%32%28%17%
792
November1st to 10thNight
12%5%11%33%30%10%
740
11th to 20thNight
12%315%34%27%8%
760
21st to endNight
12%414%37%24%8%
760
December1st to 10thNight
18%6%15%32%23%6%
760
11th to 20thNight
24%6%14%30%19%6%
760
21st to endNight
22%10%17%29%19%4
836
Page generated at 2024-01-08 08:14:19. Version ac07

Copyright 2024 Attilla Danko


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